JP3451774B2 - Tire pressure detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire air pressure detecting device for detecting a tire air pressure state based on a tire resonance frequency or a spring constant.

[0002]

2. Description of the Related Art Conventionally, as a device for detecting a tire air pressure state, a signal including a tire vibration frequency component is analyzed to extract a resonance frequency, and the tire air pressure state is detected based on the resonance frequency. There is something to do
No. 133831).

[0003]

The vibration frequency component of the tire has a plurality of resonance vibrations caused by twisting and eccentricity of the tire, which are subjected to frequency analysis (for example, FFT (fast Fourier function) calculation). By doing so, the resonance frequency is obtained, and the tire pressure can be detected based on the resonance frequency.

However, the frequency range in which the resonance vibration appears varies according to changes in the environment in which the vehicle is placed. Therefore, if only resonance vibration in a certain environment is observed, it is necessary to detect the tire air pressure. There is a problem that you can not do. For example, when the vehicle generally travels in the urban area at low to medium speeds, the resonance vibration of the tire mainly appears around 35 Hz, but when the vehicle travels at high speed,
Since the intensity of the resonance vibration around 35 Hz is lowered and the resonance frequency cannot be obtained, the tire air pressure cannot be detected.

Therefore, an object of the present invention is to detect tire air pressure even when the environment in which the vehicle is placed changes.

[0006]

In order to achieve the above object, the present invention provides an extracting means for extracting a resonance frequency from a wheel speed signal containing a vibration frequency component of a tire when the vehicle is running. (S10-S40, S60)
And a detection means (S50, S70) for detecting the state of the air pressure of the tire based on the extracted resonance frequency, in the tire pressure detection device, the extraction means (S10-S40, S60) is a vehicle speed. all SANYO extracting the resonant frequency in the selecting means (S30) comprises a selected frequency range by the selection means (S30) for selecting the frequency range of interest of the extraction of the resonance frequency according to (S40 , S60), the selecting means (S3)
0), the first frequency (f1) ~
When the first frequency range of the second frequency (f2) is selected
And the second of the third frequency (f3) to the fourth frequency (f4)
In some cases, the frequency range of
The wave number range is a frequency range deviated from the first frequency range.
The technical means of being enclosed is adopted.

According to the second aspect of the invention, the extraction means (S110 to S150, S17) for extracting the resonance frequency from the wheel speed signal containing the vibration frequency component of the tire when the vehicle is running.
0) and the detection means (S160, S1) for detecting the air pressure state of the tire based on the extracted resonance frequency.
80), the extraction means (S110 to S150, S170) divides the frequency range targeted for the extraction of the resonance frequency into a plurality of ranges, and also the signal strength in each of the frequency ranges. And a selecting means (S140) for selecting a frequency range to be extracted from the resonance frequency based on the signal strength calculated by the calculating means (S130). The resonance frequency is extracted in the frequency range selected by the selection means (S140) (S150, S17).
The technical means of 0) is adopted.

According to the third aspect of the invention, the extracting means (S210 to S260, S28) for extracting the resonance frequency from the wheel speed signal containing the vibration frequency component of the tire when the vehicle is running.
0) and the detection means (S270, S29) for detecting the air pressure state of the tire based on the obtained resonance frequency.
0) and a tire pressure detecting device including: the extracting means (S210 to S260, S280) divides the range of frequencies to be the target of extracting the resonance frequency into a plurality of ranges, and a plurality of ranges in each of the frequency ranges. Resonance in the range of each frequency based on a plurality of resonance frequencies calculated by the resonance frequency calculation means (S230) and a resonance frequency calculation means (S230) for calculating a plurality of resonance frequencies respectively. Standard deviation calculating means (S240) for calculating standard deviation of frequency
And a selecting means (S250) for selecting a frequency range targeted for extraction of the resonance frequency based on the standard deviation calculated by the standard deviation calculating means (S240). The resonance frequency is extracted in the selected frequency range (S
260, S280).

According to the invention described in claim 4, extracting means (S410 to S44) for extracting the spring constant of the tire from the wheel speed signal including the vibration frequency component of the tire when the vehicle is running.
0, S460, S470) and a detection means (S450, S480) for detecting the state of the air pressure of the tire based on the extracted spring constant, in the tire air pressure detection device, the extraction means (S410 to S440, S
460, S470) selecting means (S42) for selecting a frequency range for which the spring constant is to be extracted according to the vehicle speed.
0) for extracting the spring constant in the frequency range selected by the selecting means (S420).
Ri (S430, S440, S460, S470 ), the
According to the vehicle speed, the first means is selected by the selecting means (S420).
A first frequency range from frequency (f1) to second frequency (f2)
When the enclosure is selected, the third frequency (f3) to the fourth frequency
There is a case where the second frequency range of several (f4) is selected.
And the second frequency range is the first frequency range
Adopt technical means that the frequency range is offset .

The reference numerals in parentheses of the above-mentioned means indicate the correspondence with the concrete means described in the embodiments described later.

[0011]

According to the first aspect of the present invention, since the frequency range from which the resonance frequency is extracted is selected based on the wheel speed signal, even if the traveling speed of the vehicle changes. Tire pressure can be detected. Further, according to the invention described in claim 2, according to the invention described in claim 3, the resonance frequency is extracted based on the standard deviation of the plurality of resonance frequencies. Since each frequency range is selected, the tire pressure can be detected.

Further, according to the invention of claim 4,
Since the frequency range from which the spring constant is extracted is selected based on the vehicle speed, the tire air pressure can be detected.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a tire air pressure detecting device according to the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing the overall configuration of a tire air pressure detection device according to the present invention. As shown in FIG. 1, each tire 1a-1 of the vehicle
Wheel speed sensors 2 to 5 are provided corresponding to d.
Each wheel speed sensor 2-5 is comprised by the gearwheels 2a-5a and the pickup coils 2b-5b, respectively. The gears 2a to 5a are coaxially attached to the rotation shafts (not shown) of the tires 1a to 1d and are made of a disk-shaped magnetic body. The pickup coils 2b to 5b are attached near the gears 2a to 5a at predetermined intervals, and the gears 2a to 5a, that is, the tires 1a to 1d.
The AC signal having a cycle corresponding to the rotation speed of the is output.

AC signals output from the pickup coils 2b to 5b are sent to a known electronic control unit (hereinafter abbreviated as ECU) 6 having a microcomputer including a CPU, ROM, RAM and the like, and a waveform shaping circuit. The signal is input and predetermined signal processing including waveform shaping is performed. The result of this signal processing is input to the display unit 7, and the display unit 7 notifies the driver of the air pressure state of each tire 1a to 1d.

The display unit 7 may independently display the air pressure states of the tires 1a to 1d, or one warning lamp may be provided so that the air pressure of any one of the tires becomes lower than the reference air pressure. You may make it warn by making it light when it does. Hereinafter, a first embodiment of the tire air pressure detection device according to the present invention will be described based on the flowchart of FIG. 3 showing the processing contents of the ECU 6. It should be noted that the ECU 6 performs the same processing on each of the tires 1a to 1d, and therefore the flowcharts in the following embodiments show only the processing on the tire 1a.

First, in step S10, a pulse signal obtained by waveform-shaping the AC signal output from the pickup coil 2b is read, the pulse length is divided by the pulse time, and the wheel speed V is calculated. The wheel speed V
The calculation of may be performed for only one wheel, or may be performed by calculating the average value of four wheels. Next, in step S20, frequency analysis by FFT (Fast Fourier Function) calculation is performed on the calculated wheel speed V to calculate the signal strength for each frequency.

From the detailed study by the present inventors, it was found that the resonance vibration of the tire has the following characteristics. That is, in the low to medium speed range where the vehicle travels in the city, the power spectrum of the wheel speed with respect to each frequency is as shown in FIG. 3A, and the resonance vibration of the tire appears near about 35 Hz. However, in a high speed region such as traveling on a highway, as shown in FIG. 3 (b), the power spectrum of the resonance vibration appearing in the vicinity of about 35 Hz becomes extremely small, so that it cannot be detected.

On the other hand, the power spectrum of other resonance vibrations of the tire appearing in the vicinity of about 70 Hz is small in the low to medium speed region as shown in FIG. 3 (c), but as shown in FIG. 3 (d). , Becomes larger in the high-speed area. Further, both of these resonance vibrations have a unique relationship with the tire air pressure because the resonance frequency of the two resonance vibrations decreases as the tire air pressure decreases.

Therefore, in order to detect the resonance vibration regardless of the traveling speed of the vehicle by using such a relation, the calculated wheel speed V (currently traveling speed) is previously determined in step S30. It is determined whether or not the vehicle speed is smaller than a predetermined wheel speed VS that has been set, that is, whether the traveling speed of the vehicle is in the low to medium speed region or the high speed region. Then, if it is determined that the wheel speed V is smaller than the reference wheel speed VS, that is, if the traveling speed of the vehicle is in the low to medium speed range, the process proceeds to step S40, and the resonance vibration exists near 35 Hz f1. .About.f2 (for example, 20 Hz to 60 Hz), the resonance frequency FkL of the resonance vibration is calculated a plurality of times based on the result of the FFT calculation in step S20, and the average value of the resonance frequencies is calculated.

Then, in step S50, the air pressure P is calculated from the relationship between the resonance frequency and the air pressure shown in FIG. 4A based on the detected resonance frequency FkL. The relationship between the resonance frequency and the air pressure is shown in a map of the ECU.
It is stored in the ROM or the like. Next, step S80.
In step S50, it is determined whether or not the air pressure P calculated in step S50 is less than or equal to a preset allowable lower limit value Pd of the air pressure, and the air pressure P is set to a preset allowable lower limit value Pd.
If the following is determined, the process proceeds to step S90, and a predetermined warning display is performed.

On the other hand, in step 30, the wheel speed V
Is determined to be equal to or higher than the predetermined wheel speed VS, that is, when the vehicle traveling speed is in the high speed region, the process proceeds to step 60, and the resonance vibration of the tire appearing in the vicinity of 70 Hz is targeted for detection. Frequency range f3 to f4
(For example, 60 Hz to 100 Hz), the resonance frequency FkH of the resonance vibration existing in the frequency range is calculated plural times, and the average value of the resonance frequencies is calculated. Then, in step S70, the detected resonance frequency Fk.
Based on H, the air pressure P is calculated from the relationship between the resonance frequency and the air pressure shown in FIG. Thereafter, the determinations and processes of steps S80 and S90 are performed in the same manner as described above, and a predetermined alarm display is performed.

As described above, according to the tire pressure detecting device of this embodiment, even if the traveling speed of the vehicle changes,
The tire air pressure can be detected by extracting the resonance frequency suitable for calculating the air pressure. Note that steps S10-4
0, S60 is the extraction means, S30 is the selection means, and S50
And 70 correspond to detection means, respectively.

Next, a second embodiment of the tire pressure detecting device according to the present invention will be described with reference to FIG.
A description will be given based on the flowchart. Note that, here, an example in which the sum of gains of the power spectrum is used as the strength of resonance vibration will be described. First, in step S110, the wheel speed V is calculated as in step S10 of the first embodiment. Then, in step S120, the FFT calculation is performed on the calculated wheel speed V to calculate the power spectrum for each frequency. Next, in step S130, the gain sum EL of the power spectrum in the frequency range f1 to f2 that can cover the resonance frequency (around 35 Hz) that appears mainly during low-speed running, and the resonance frequency (around 70 Hz) that mainly appears during high-speed running are covered. The total gain EH of the power spectra in the frequency range f3 to f4 that can be calculated is calculated.

Then, in step S140, it is determined whether or not the calculated sum of gains EL of the power spectrum is larger than the calculated sum of gains EH of the power spectrum, and the one with the larger sum of gains is used to detect the tire air pressure. The target frequency range is. Gain sum E
When it is determined that L is larger than the total gain EH, it is estimated that there is a strong resonance vibration in the range of the frequencies f1 to f2, and therefore the process proceeds to step S150, the same as step S40 of the first embodiment. Frequency range f1 to
The resonance frequency FkL existing in f2 is calculated a plurality of times, and the average value of those resonance frequencies is calculated. And step S
At 160, based on the detected resonance frequency FkL as in step S50 of the first embodiment, FIG.
The air pressure P is calculated from the relationship between the resonance frequency and the air pressure shown in.

Next, in step S190, it is determined whether or not the air pressure P calculated in step S160 is less than or equal to a preset allowable lower limit value Pd, and the air pressure P is set in advance. If it is determined to be equal to or less than Pd, the process proceeds to step S190, and a predetermined alarm display is performed. On the other hand, when it is determined in step S140 that the total gain EH is larger than the total gain EL, it is estimated that resonance vibration with high intensity exists in the range of frequencies f3 to f4, and thus the process proceeds to step S170 and the frequency range f3 to The resonance frequency FkH of the resonance vibration existing in f4 is calculated a plurality of times, and the average value of these resonance frequencies is calculated. Then, in step S180, the air pressure P is calculated from the relationship between the resonance frequency and the air pressure shown in FIG. 4B based on the detected resonance frequency FkH. Thereafter, similarly to the above, the processes of steps S190 and S200 are performed, and an alarm is displayed.

As described above, according to the tire air pressure detecting apparatus of this embodiment, among the resonance vibrations of a plurality of tires that appear, the frequency range in which the resonance vibration having the large sum of gains of the power spectrum exists is taken as the extraction target of the resonance frequency. Therefore, the tire air pressure can be detected even if the traveling speed changes and the frequency band to be detected changes. Note that steps S110 to 150 and S170 are extraction means, and S1
30 corresponds to the calculating means, S140 corresponds to the selecting means, and S160 and 180 correspond to the detecting means.

Next, a third embodiment of the tire pressure detecting device according to the present invention will be described with reference to FIG.
A description will be given based on the flowchart. First, in step S210, the wheel speed V is calculated as in step S10 of the first embodiment. Then, step S22
At 0, the FFT calculation is performed on the calculated wheel speed V. Next, in step S230, in the frequency range f1 to f2 capable of covering the resonance vibration (near 35 Hz) that appears during low speed traveling, the resonance frequency Fk
The resonance frequency FkL is calculated a plurality of times by performing the calculation for obtaining L a plurality of times to calculate a plurality of resonance frequencies FkL, and similarly, in f3 to f4 that can cover the resonance vibration (around 70 Hz) that appears when traveling at high speed. To do.

Then, in step 240, the standard deviation σFkL of the resonance frequency FkL calculated a plurality of times and the standard deviation σFkH of the resonance frequency FkH are calculated. Next, in step S250, the standard deviation σFk
L and the standard deviation σFkH are compared, and the one with a smaller value, that is, the one with a stable frequency magnitude is targeted for tire pressure detection. Here, if it is determined that the standard deviation σFkL is smaller than the standard deviation σFkH, step S
Proceeding to 260, a plurality of resonance frequencies FKL are selected, and the average value of those resonance frequencies is calculated.

That is, the smaller the standard deviation, the greater the frequency stability, and the accurate resonance frequency can be extracted. Then, in step S270, the air pressure P is calculated based on the resonance frequency FkL from the relationship shown in FIG. 4A, as in the first embodiment, and step S300.
At, it is determined whether the air pressure P is less than or equal to the allowable air pressure Pd. Then, if it is determined that the air pressure P is less than or equal to the allowable air pressure Pd, a predetermined alarm display is performed in step S310.

On the other hand, if it is determined in step S250 that the standard deviation σFkH is smaller than the standard deviation σFkL, the process proceeds to step S280, where the plurality of resonance frequencies FKH.
Is selected, and the average value of those resonance frequencies is calculated. Then, in step S290, the air pressure P is calculated based on the resonance frequency FkH from the relationship shown in FIG.
In step S300, it is determined whether or not the air pressure P is less than or equal to the allowable air pressure Pd, and similarly to the above, step S310.
A predetermined warning is displayed at.

As described above, according to the tire pressure detecting device of this embodiment, since the resonance frequency having the higher stability is selected, the tire pressure can be accurately detected regardless of the traveling speed of the vehicle. You can As an index showing the stability of the resonance frequency, in order to simplify the processing in the ECU, the range from the maximum value to the minimum value of the resonance frequency obtained by multiple calculations, The difference between the resonance frequency obtained by the above calculation and the resonance frequency obtained this time may be used. Steps S210 to 260, S
280 corresponds to extraction means, S230 corresponds to resonance frequency calculation means, S240 corresponds to standard deviation calculation means, S250 corresponds to selection means, and S270 and 290 correspond to detection means.

Next, a fourth embodiment of the tire air pressure detecting device according to the present invention will be described with reference to FIG.
A description will be given based on the flowchart. First, in step S410, the wheel speed V is calculated as in step S10 of the first embodiment. And step 420
The current wheel speed V is set to the preset wheel speed V
It is determined whether it is smaller than S, that is, whether the vehicle is traveling at low speed or at high speed. If it is determined that the vehicle is traveling at low speed, the process proceeds to step 430, and the frequency range of f1 to f2 (around 35 Hz) in which the power spectrum of the wheel speed largely appears during traveling at low speed.
And a wheel speed signal is filtered using a bandpass filter. This filtering is performed in order to remove unnecessary high frequency noise and accurately calculate the tire spring constant from the wheel speed.

Next, at step 440, the spring constant KL is estimated and calculated from the wheel speed signal passed by the filtering. This calculation is performed according to the following equation 1.

[0034]

## EQU1 ## K = -J1 (dω1 / dt) / (∫ω1dt) Here, K is a spring constant, and ω1 is an angular velocity detected and calculated by the pickup coils 2b to 5b in FIG. That is, the spring constant KL can be calculated based on the wheel speed. The spring constant KL may be calculated by calculating a plurality of spring constants on the basis of a plurality of wheel speed signals in the frequency range of f1 to f2 and taking an average value thereof, or in the frequency range of f1 to f2. It may be calculated based on the maximum wheel speed signal.

By the way, the spring constant and the air pressure have the relationship shown in FIG. FIG. 8A shows the relationship between the air pressure and the spring constant KL during low speed running, and FIG. 8B shows the relationship between the air pressure and the spring constant KH during high speed running. The relationship between these spring constants and air pressure is EC in the form of a map.
It is stored in the U ROM or the like. And step S
At 450, the air pressure P is calculated based on the spring constant calculated by the above calculation and the relationship shown in FIG. Next, in step S490, it is determined whether or not the calculated air pressure P is less than or equal to a preset air pressure Pd. If it is determined that the air pressure Pd is less than or equal to the air pressure Pd, the process proceeds to step S500, and a predetermined alarm is displayed. To do.

On the other hand, if it is determined in step S420 that the current wheel speed V is not lower than the preset wheel speed VS, that is, that the vehicle is traveling at high speed, the process proceeds to step S460, and the power spectrum of the wheel speed during high speed traveling. Is selected and the frequency range of f3 to f4 (around 70 Hz) is selected and filtered. Then, in step S470, the spring constant KL is estimated and calculated from the wheel speed signal passed by the filtering based on the arithmetic expression of the equation 1, and in step S480, FIG.
The air pressure P is calculated from the relationship between the spring constant and the air pressure shown in (b). Next, similarly to the above, a predetermined alarm display is performed through steps S490 and S500.

As described above, according to the tire pressure detecting device of this embodiment, the tire pressure is accurately detected and an alarm is displayed regardless of whether the vehicle is running at a low speed or a high speed. be able to. It should be noted that it is possible to calculate a plurality of spring constants by performing a plurality of calculations in each frequency range, calculate their standard deviations, and calculate the spring constants to be calculated based on the magnitude of the standard deviations. It is also possible to select a possible frequency range. Steps S410 to S440, S460 and S470 are extraction means, S420 is selection means, and S4.
50 and S480 correspond to the detection means, respectively.

Further, step S30 of the first embodiment.
In step S420 of the fourth embodiment, the traveling speed range is determined based on the wheel speed. However, the vehicle speed signal detected by the speed sensor provided in the vehicle mission or the vehicle speed signal before and after the vehicle speed signal is provided. The determination may be made based on the vehicle speed signal obtained by integrating the acceleration signal detected by the acceleration sensor.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of a tire air pressure detection device according to the present invention.

FIG. 2 is a flowchart showing a process in an ECU in the first embodiment.

FIG. 3 is a graph showing power spectra of wheel speeds during high speed traveling and low speed traveling.

FIG. 4 is a graph showing the relationship between tire air pressure and resonance frequency.

FIG. 5 is a flowchart showing a process in an ECU in the second embodiment.

FIG. 6 is a flowchart showing a process in an ECU according to a third embodiment.

FIG. 7 is a flowchart showing a process in an ECU according to a fourth embodiment.

FIG. 8 is a graph showing the relationship between tire air pressure and tire spring constant.

[Explanation of symbols]

1a to 1d ... Tire, 2a to 5a ... Gear, 2b to 5
b ... Pickup coil, 2-5 ... Wheel speed sensor, 6 ... ECU, 7 ... Display section.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Motoji Suzuki, 1-1, Showa-cho, Kariya city, Aichi, Nihon Denso Co., Ltd. (56) References JP-A-8-156536 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01L 17/00 B60C 23/00

Claims (4)

(57) [Claims] 1. Extraction means for extracting a resonance frequency from a wheel speed signal including a vibration frequency component of a tire when the vehicle is running, and detection means for detecting a tire air pressure state based on the extracted resonance frequency. In the tire air pressure detection device having the above, the extraction means includes a selection means for selecting a frequency range to be the target of the extraction of the resonance frequency according to a vehicle speed, and the resonance frequency in the frequency range selected by the selection means. der extracts a is, by the selection of the selecting means, a first frequency-depending on the vehicle speed
When the first frequency range of the second frequency is selected,
A second frequency range from 3 frequencies to 4 frequencies is selected.
In some cases, the second frequency range is equal to the first frequency range.
A tire air pressure detection device having a frequency range deviating from the wave number range . 2. Extraction means for extracting a resonance frequency from a wheel speed signal containing a vibration frequency component of a tire when the vehicle is running, and detection means for detecting a tire air pressure state based on the extracted resonance frequency. In the tire pressure detection device having the above, the extraction means divides the frequency range targeted for the extraction of the resonance frequency into a plurality of ranges, and a calculation means that respectively calculates the signal strength in each of the frequency ranges, and the calculation. Selecting means for selecting a frequency range to be the target of extracting the resonance frequency based on the signal intensity calculated by the means, and extracting the resonance frequency in the frequency range selected by the selecting means. A tire pressure detection device characterized by the above. 3. Extraction means for extracting a resonance frequency from a wheel speed signal containing a vibration frequency component of a tire when the vehicle is running, and detection means for detecting a state of air pressure of the tire based on the obtained resonance frequency. In the tire air pressure detection device provided with, the extraction means, while dividing the range of frequencies to be the target of the extraction of the resonance frequency into a plurality of ranges, performs a plurality of calculations in each of the frequency ranges to determine a plurality of resonance frequencies. Resonant frequency calculating means for calculating respectively, standard deviation calculating means for calculating the standard deviation of the resonance frequency in each frequency range based on the plurality of resonance frequencies calculated by the resonance frequency calculating means, and the standard deviation Based on the standard deviation calculated by the calculating means, a selection for selecting the frequency range to be the target of extracting the resonance frequency A tire air pressure detecting device, comprising: a determining unit for extracting the resonance frequency in the frequency range selected by the selecting unit. 4. Extraction means for extracting a spring constant of the tire from a wheel speed signal including a vibration frequency component of the tire when the vehicle is traveling, and detection for detecting a state of air pressure of the tire based on the extracted spring constant. In the tire air pressure detecting device including means, the extracting means includes a selecting means for selecting a frequency range to be a target of extraction of the spring constant according to a vehicle speed, and in the frequency range selected by the selecting means, all SANYO for extracting the spring constant, by the selection of the selecting means, a first frequency-depending on the vehicle speed
When the first frequency range of the second frequency is selected,
A second frequency range from 3 frequencies to 4 frequencies is selected.
In some cases, the second frequency range is equal to the first frequency range.
A tire air pressure detection device having a frequency range deviating from the wave number range .